In microwave equipments, such as filters, oscillating circuits, resonators etc., trimming screws are used to tune and adapt the frequency. Generally, the trimming screw is secured with a locknut after the tuning. In an ordinary screw joint, e.g. in a filter or the like, occurs a certain amount of play between the thread and the screw, which effects the trimming of the filter. Moreover, when the locknut is tightened to secure the screw joint, the tuning is effected.
Since the frequency tuning is significant for the function of a microwave filter or the like, an incorrect tuning, even with very small variation, may consequently effect function of it and other devices enclosed in a microwave transmitter/transponder/receiver. It is therefore important that the trimming screw can be screwed so that an exact desired tuned position can be obtained and that the screw maintains its position and it is not influenced by the changes in the temperature, vibrations and so on. Moreover, parts of many devices are made of material, such as plastic, which makes the production of threads of small dimensions difficult in the material.
JP 5-152845 describes an oscillating circuit cover of which is manufactured of plated plastic material. A trimming screw corresponding to the position of a dielectric resonator is arranged in the ceiling of the cover by screwing it in a tubular metallic nut. The nut is cast in one piece with the cover. The screw is not secured.
Securing the trimming screw or device is known, for example through DE-A1-40 26 062, in which a trimming bolt is connected to a screw which dislocates it. The screw is fixed by a clamp nut pressing a conical flexible insert against the screw.
In U.S. Pat. No. 4,794,354 a locking insert of rubber is used to maintain a screw connected to a resonance element by means of a bar.